Piezo-electric frequency eliminator



Jan. 7, 1930. w. H. T. HOLD EN PIEZO ELECTRIC FREQUENC ELIMINATOR Filed. D60. 51. 1926 Ra s INVENTOR. WETHOZdB/fl/ ATTORNEY Patented Jan. 7, 1930 UNITED STATES PATENT OFFICE WILLIAM H. '1. HOLDEN, 0F BROOKLYN,

NEW YORK, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION on NEW YORK FIRED-ELECTRIC FREQUENCY ELIMINATOR Application filed December a1, 1926. Serial No. 158,322.

" These interfering or undesirable frequencies may emanate from radio telegraph stations, and may be present in the quencies which lie within the limits of the band to be transmitted. Special circuits'have' heretofore been developed for balancing out these undesirable or interfering frequencies, but these are only partly successful in practice because they require very frequent adjustments to compensate for changes in the phase and in the magnitude of the undesired or interfering current. Moreover, the absorption of such frequencies by resonant circuits, for example, tuned thereto is very diflicult.

An insurmountable objection to the use of tuned circuits as absorbing elements is apparent from the well-known frequency characteristics of tuned circuits which are so broad as to absorb an appreciable part of the signal band along with the undesirable or interfering frequencies.

Accordingly, it is an object of this invention to provide a'piezo-electric device to flirnish an absorbing circuit sufiiciently sharp in its frequency characteristic asto have a comparatively small or negligible effect on a band of signals to be transmitted. -Moi'eover, wherever there are two or more undesirable, frequencies, or, in general, wherever there are two or more undesirable bands of frequencies, it is an object of this invention to provide two or more of such piezo-electric devices to act as the absorbing bodies, one corresponding to each undesirable wave or to each undesirable hand, these piezo-electric devices functioning independently.

It is another object of this invention to so relate elements of reactance to the piezo-elec system at fretric devices that the absorbing circuits, which include the piezo-electric devices and the corresponding reactance elements, will have a. very low or a minimum of impedance at the undesirable frequencies.

While this invention will be pointed out with particularity in the appended claims, the invention itself, both as to its further objects and features, will be better understood from the detailed description hereinafter following when read in connection with the accompanying drawing, in which Figure 1 represents one embodimentof the invention, shown merely for the purpose of illustration; Fig. 2 shows a reactance curve vice, and Fig. 3 shows the reactance curve of a piezo-electric device, the form of which is modified by suitable reactance elements.

Referring to Fig. 1 of the drawing, a

of a piezo-electric desource S represents diagrammatically any 7 source for supplying currents having various frequencies. such as a telephone system, one or more of the frequencies of which are to be substantially suppressed. The source S supplies currents to the vacuum tube V 7 which may be of the three-electrode type, throug a transformer T The grid of the vacuum tube V may be maintained at a suitable negative potential by means of a battery B The is supplied with space current b a battery B through a choke coil L. Another vacuum tube V is connected in tandem with the vacuuip tube V The battery B, provides the grid of the latter vacuum tube, sistance R, with suitable negative potential. A condenser G5 has one terminal directly connected to-the plate of the vacuum tube V and another terminal directly connected plate of the vacuum tube'V through reto the grid of the vacuum tube V and serves,

The plate of the rents, in the plate circuit of the vacuum tube i 2 are transmitted to an output circuit S through transformer T Batteries B and in an exceedingly small range of the fre- B heat the filaments of the vacuum tubes V quen cy spectrum, the change taking place and V respectively, to electron-emitting about the frequency corresponding to the temperatures, the negative terminals of these point a. As the frequency increases, the 5 batteries being grounded. Obviosuly, a sinpiezo-electric, device exhibits a capacitative gle batterymay replace batteries 13.; aiid B reactance of a, decreasing order. Two absorbing circuits are connected from Fig, 3 howsanoth r reactance curve of the/right-hand terminal of the condenser C a piezo-electric d vice, odified du to the to ground. These absorbing ir minterpositionmofsuitable reactance. In the 10 prise piezo-electric devices P13 and PEZ, and case taken for illustrative purposes, the resuitable reactance elements shown herein as eetanee comprises a i it B t- "ariahle Condensers 1 and 2, e p yting capacity in series with the piezo-elec- A ire uency o'r frequencies, wh1ch may b tric device, an arrangement can be provided undesira 1e, may lie Within h b bands which never exhibits an inductive reactance,

15 of signals to be transmitted by the system. hi h h t th t, a mall induc- 8e The a s ng Circuits e p g t P tive reactance. In the arrangement having electric devices and the correspondlng series th reaetahee curve Shown i Fi 3 th re leaetallee elements are ihtledueee Provide actance never attains an inductive value. means for substantially suppressing the un- Th k f th reactance u v in Fig. 3

2e desirable wave or Wav SO that thell efieets coincides with the line of zero reactance, up n h bands o slgnals he tl'ehshlltted and, at the frequency corresponding to this by the system will be substantially eliminated, k d t frequencies dj t t th h as will be shown more fully hereinafter. All quency o di t th ak, the arfrequencles e mlI g 1 ff0m h P 1 rangement will have a minimum of imped- 25 are Impressed Oh the lhpht elrehltof the ance, while at other frequenciessubstantially vacuum tube V through the transformer T diff e t f th frequency eel-responding These voltages are amplified 1n a nanner well to h peak, h im a ill b hi h, known, In the art t PP 1h Ph Such an arrangement shunted across one of form 111 the Output h of the Vacuum the circuits of a transmission system will :0 tube l' Thesefrequencles P through the greatly attenuate and, in effect, substantially e e o and are lmpressed Oh the Input suppress the frequency corresponding to the circuit of th vacuum tllhe z- These minimum impedance of the erystal as well (lheheles are further hP h y e h as a small bandof frequencies immediately tube 2 and pp 1h output C1rcu 1t7 adjacent the latter frequency. In Fig. 1, k

5 whereupon they are transmitted to the C1I'- h id i i f th vacuum t b ,V i

e 2 e gh e transformer 2 designed to have a high impedance as com- The series c1rcu1ts compr1s1ng the piezopared to the bi d impedance f th i electric devlees and the eonespohdlhg reac" zo-electric device and the associated reactive tive elements are arranged so as to have very l t 40 Small g g b hhPedeheeS' at the It will be understood that while only two- 106 quencies wh ch are to be suppre s d- G111 vacuum tubes have been shown herein in an Tehh PP 1n the Output ehclht of the amplifyin system, any number of vacuum Vacuum tube 11 that e P frequency equal tubes may be similarly connected, in which. to h eq e y at Whleh oheof these suitable combinations of piezo-electric de- 45 serblng ellelllts h a y low lmpedance he-vices and reactive elements may be associ- 110 compared to the lmpedahee between e g ated to substantially suppress a-plurality of and fil m n 0f the Vacuum h Q be single frequencies or a plurality of bands of shunted through that absorbing c1rcu1t, S frequencies without materially affecting the that 1ts effect upon he n hands gtransmission or amplification of other he 50. nals to be transm tted by the system W111 'be uencies or other bands of frequencies. It 115 substantially suppressed. will be distinctly understood that although Fig. 2 represents a ehaiae r real? the absorbing circuits have been illustrated ltane Of a plezo-eleetrleerystelh as connected between the grid and filament curve indicates that s e fr q e y of one of the vacuum tubes, the object of this as pressed across the piezo-electric crystal 1ni ti may b d t b connecting creases, the reactance is apa ltati and 0f the absorbing circuits at other points in the a. decreasing order. At the frequency COIIB- system, as for example between the plate sponding to point 6, the reactance is zero,and d fil t f a a m tub at frequencies somewhat higher than the fre- The sharpness of a piezo electric device 60 quency corresponding to point 72, th eis particularly advantageous for the suppres tance becomes inductive and increases at a sion of undesirable frequencies, because the rather rapid rate until the inductive reactance l ctrical circ it h r tof 1 v d' f reaches its maximum value. Thereafter, the thi purpo e have b inh tl hf neh reactance changes from a very high inductive high decrement that a considerable range of 65 value to a very high capacitative value Withfrequencws on elther side of the undesired frequencies were also substantially suppressed. The use. of a piezo-electric device without a reactance element of suitable magnitude may lead to oscillation at the frequency intended for suppression. If, in the example of Fig. 1, the reactance of the plate circuit of the vacuum tube V bears a defi-. nite relationship to the reactance in the grid circuit of that vacuum tube at the particular frequency involved, that frequency will be transmitted. Obviously, by rendering the reactance of the crystal circuit capacitative, or, at the most, only slightly inductive, it will be clear that the undesired frequency or frequencies will be substantially suppressed, and their effects upon the other frequencies will be nullified. It is to be noted that a further reduction in the amplitude of an undesirable frequency may be attained by introducing regeneration so as to compensate for the unnecessary and unavoidable resistance (due to the viscosity and damping of the crystal), and accordingly still further reduce its effective impedance by the negative resistance introduced by the regeneration.

The term piezo-electric (as employed herein) refers to that property of a body or substance by which an electro-motive the effect of a plurality force results from mechanical stress, and vice versa.

While this invention has been shown in one particular embodiment, merely for the purpose of illustration, it will be clearly understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. The method of substantially eliminating the effect of a plurality of undesirable frequencies which lies within the limits of a band with a plurality of mechanically vibrating bodies and a plurality of reactive elements, one mechanically vibrating body and one .reactive element corresponding to each of the undesirable frequencies, which consists in vibrating said plurality of mechanically vibrating bodies, and so controlling the magnitude of the reactances of the various reactive elements that the undesirable frequencies will become absorbed therein.

2. The method of substantially eliminating of undesirable frequencies which lie Within the limits of a band with a plurality of piezo-electric bodies, one corresponding to each undesirable frequency, which consists in vibrating said plurality of piezo-electric bodies, and substantially decreasing the magnitude ofthe reactance of each piezo-electric body at the corresponding undesirable frequency so that each piezoelectric body forms a path of low impedance for said corresponding undesirable frequency.

parallel paths of low impedancefor the respective frequencies to be substantially suppressed.

4. The combination of means for generating a band of signals, an amplifying system foramplifying said band of signals, a piezoelectric device, and a reactive element, said piezo-electric device and said reactive element being coupled to the amplifying system so that all frequencies within a small portion of said band will be substantially suppressed without disturbing the nature of the band of signals being amplified.

5. The combination of a source of speech signals, means for transmitting said speech signals, a band of undesirable frequencies being superposed on said speech signals and emanating from said source, a piezo-electric device, and means co-operating with said piezoelectric device and coupling said piezoelectric device with said transmitting means to render said piezo-electric device of low impedance and consequently absorbent to said band of undersirablefrequencies.

6. -':A system for substantially eliminating a plurality of undesirable frequencies which are superposed upon a band of frequencies corresponding to speech signals, comprising a plurality of piezo-electric bodies upon which are impressed said band of frequencies corresponding tospeech signals as well as the superposed undesirable frequencies, one piezo-electric body corresponding to each superposed frequency, and a plurality of re active elements, one reactive element being coupled to each piezo-electric body and cooperating with each piezo-electr-ic body so as to render the magnitude of the reactance substantially negligible, whereupon the superposed frequencies becoine substantially sup pressed. I

7. A system forsubstantially suppressing a plurality of undesirable frequencies which lie within the limits of a band corresponding to speech signals, comprising a plurality of piezoelectric devices, one plezo-electric device corresponding to each undesirable frequency, and a plurality of reactive elements, one corresponding to each piezo-electric body, each reactive element being coupled to a piezoelectric device so as to render its reactance neglible at a particular undesirable frequency, whereupon the undesirable frequencies become absorbed without any substantial distortion of the band.

l cember, 1926.

8. A system for substantially eliminating the effect of a plurality of interferin frequencies which lie within the limits of a band, comprising a plurality of electro-mechanical vibrating bodies, and a plurality of reactive elements, one corresponding to each electromechanical vibrating body, each reactive element being coupled to the corresponding electro-mechanical body and rendering theJ electro-mechanical body to which it'corresponds of low impedance at one of the interfering frequencies.

In testimony whereof,v I have signed my name to this specification this 29th day of De- WILLIAM H.- TIHOLDEN. 

